Nominal Metonymy Processing

We argue for the necessity of resolution of metonymies for nominals (and other cases) in the context of semantics-based machine translation. By using an ontology as a search space, we are able to identify and resolve metonymic expressions with significant accuracy, both for a pre-deterrnined inventory of metonymie types and for previously unseen cases. The entity replaced by the metonymy is made explicitly available in our meaning representation, to support translation, anaphora, and other mechanisms. 1. I n t r o d u c t i o n Lakoff and Johnson (1980) identify metonymy as "using one entity to refer to another that is related to it." Following Gibbs (1993), we distinguish metonymy from metaphor in that metonymy uses an entity to refer to another, related, entity from the same domain, whereas metaphor necessarily relies on the replacement of an entity from one domain by an entity from another conceptual domain. As has been well-established in the literature, metonymic language use is pervasive in written and spoken language. NLP efforts addressing specific corpora, such as Hobbs and Martin (1987), Stallard (1993), and MADCOW (1992), all had to address metonymic phenomena because of its high frequency. The training and test data collected for this effort (as described below) also found high volumes of metonymy in newswires in English and Spanish. Our investigation found that the vast majority of all metonymies encountered involve the substitution of one nominal by another 1, and, given the pervasive nature of the phenomenon, we believe that semantic interpretation of nominals in context unavoidably involves metonymic resolution. 2. W h y Resolve Metonymy? We find that we need to identify and resolve metonymy during the semantic analysis phase of Machine Translation for a number of reasons, given below. (Of course, some of these arguments assume that the generation component of the MT system is able to take advantage of the additional inferences and information that is provided as a result of the resolution.) • The most compelling argument for resolving metonymy as part of the analysis process in MT is that metonymies do not necessarily translate literally into other languages. Although often they do translate felicitously, an informal investigation into the translatability of 15 examples of metonymy easily found a number of cases where a literal translation would be bizarre, misunderstood, or just ill formed. For example, in The newspaper fwed the editor in chief, the word for newspaper (shinbun) must be rendered as newspaper company (shinbunsha) to make the example understandable in Japanese. These results are consistent with the more thorough field work in Karnei and Wakao (1992) and Wakao and Helmreich (1993) on English, Chinese, and Japanese; they cite additional examples, such as He read Mao being unacceptable in Chinese. Other work by Kayser (1988) and by Horacek (1996) illustrates cases where well-formed metonymies in English are unacceptable in French or German. • In addition to the cases where literal translation of metonymy is unacceptable, there are numerous other examples where the literal translation is understandable but not fluent. • The replaced entity may need to be available for anaphoric and other referential mechanisms. In the 1. The non-nominal metonymic examples that we encountered, such as spend money used as a metonym for go shopping, often fall deeply in the grey area between metaphor and metonymy.